Electronic computing devices have become increasingly important to data computation, analysis and storage in our modern society. Modem direct access storage devices (DASDs), such as hard disk drives (HDDs), are heavily relied on to store mass quantities of data for purposes of future retrieval. As such long term data storage has become increasingly popular, and as the speed of microprocessors has steadily increased over time, the need for HDDs with greater storage capacity to store the increased amount of data has also steadily increased.
Consequently, there are seemingly constant development efforts to improve the areal density of the media implemented in hard disk drives, where the areal density is typically measured as the product of bits per inch (“BPI”) and tracks per inch (“TPI”). BPI refers to the number of bits that can be written and later reread per linear inch along a track, whereas TPI refers to the number of individual tracks per radial inch. Improvements in areal density in turn lead to higher demands and stricter requirements put on the corresponding magnetic read/write heads. Furthermore, additional and significant improvements are taking place which fundamentally change how HDDs record data onto the media, such as with perpendicular magnetic recording (PMR) and thermally assisted recording (TAR).
When a recording (“write”) element of a read/write head writes data to a magnetic disk media, non-magnetized areas are left along both sides of the data track, within the boundaries of the track. This non-magnetized area between the data tracks is referred to as “erase band.” Erase band width is an important performance parameter for determining the track density of a head, especially in view of the improvements in areal density which result in very narrow data tracks. Additionally, erase band also affects the HDD servo design and performance. Therefore, it is important to characterize and minimize the erase band of a read/write head in HDD development and to measure the erase band quickly and accurately in head production.
Triple Track Testing
It is typical for an HDD developer or manufacturer to characterize the performance of a magnetic read/write head in a number of ways using a number of respective head profiles. FIG. 3A is a graph illustrating a full-track profile 310, according to a typical 3T procedure. A full-track profile, such as full-track profile 310, is often used to determine the magnetic write width (MWW) of a head, whereby the MWW is measured or computed at 50% of peak amplitude of the full-track profile. FIG. 3B is a graph illustrating a micro-track profile 320, according to a typical 3T procedure. A micro-track profile, such as micro-track profile 320, is often used to determine the magnetic reader width (MRW) of a head, whereby the MRW is measured or computed at 50% of peak amplitude of the micro-track profile. With the MWW and MRW values, a total erase band associated with a particular head can be computed, for example, using a triple-track test (3T) procedure. Note that the erase bands can vary at different tracks on a disk media based in part on the skew angle of the head at the different tracks. Thus, erase bands may be computed at various locations, or tracks, on the disk.
A 3T procedure typically involves writing two data tracks at a certain distance apart and erasing a track between the two written tracks, thereby leaving three tracks to work with (thus, the moniker “triple-track”). Due to the erase bands associated with a recording head, erasing the middle track is performed to affect the written tracks, i.e., via the erase bands. Based on the three tracks, a triple-track test profile is constructed, from which a “total” erase band width corresponding to the particular head or head design is computed. The “total” erase band width refers collectively to the width of both erase bands associated with a track (e.g., the left and right sides of a track), which corresponds to the particular read/write head at the particular skew angle associated with the track.
FIG. 3C is a graph illustrating a triple-track test (3T) profile 330, according to a typical 3T procedure. From the 3T profile 330, one can compute the off-track read capability (OTRC) corresponding to a head. Recall that the MWW and the MRW are typically computed for the head, e.g., using full-track and micro-track profiles, respectively. Hence, based on the OTRC, MWW, and MRW, the total erase band width (2 EB) can be computed. In reference to the example 3T profile 330, the following equation can be used to compute the total erase band width:2 EB=MRW+2 OTRC−MWW  (1),where the 2 OTRC factor is essentially computed as the width of the “valley” between the two written tracks after the effect of the middle erase track.
However, a typical 3T procedure such as the foregoing does not provide the separate erase band widths associated with the track, i.e., the left side (inner diameter) erase band width and the right side (outer diameter) erase band width.